Note: Descriptions are shown in the official language in which they were submitted.
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MN-10-2110
WASHER PRESS WITH MULTIPLE NIPS AND MULTIPLE DISPLACEMENT
WASH ZONES AND METHOD
BACKGROUND OF THE INVENTION
1. Cross Related Application.
[0001] Deleted
2. Technical Field.
[0002] The present invention relates to a method and apparatus for washing and
dewatering a liquid suspension of solid biological pulp material having a wide
range of
solids concentrations, comprising a mechanical or pressurized distributor
connected to a
press washer having multiple nips and multiple washing zones.
3. Related Art.
[0003] In industries engaging in the production of pulp from solid biological
material, such as papermaking pulp from cellulosic fibers, it is known to wash
liquid pulp
suspensions in order to remove organic and inorganic impurities. Washing a
liquid pulp
suspension typically involves flushing the suspension with water or another
liquid
(washing) and then removing, or simultaneously removing, at least a part of
the water in
the suspension (dewatering). The dewatered liquid carries away impurities
contained in
the pulp suspension.
100041 Four basic types of conventional pulp washers include: drum washers
with vacuum Filters; belt washers with filter belts or double wire presses;
diffusers for
displacement washing in a tower; and washer presses in which the pulp
suspension is
dewatered only to a certain solids concentration. The present invention
relates to the field
of washer presses.
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[00051 Conventional washer presses typically comprise one or two rotatable,
cylindrical drums having perforations or slots capable of receiving wash
liquid. The drum
or drums are arranged and mounted within a correspondingly-shaped housing. The
sides
of the drum housing, more commonly referred to as the vat, extend partially
about the
surface of the drum or drums. For example, in twin-drum configurations, the
drums are
positioned side-by-side within a single vat, which usually extends about 180
degrees of the
circumference of each drum. Conventional washer presses also typically include
a feed
distributor (or feeder) located near the top of the vat for introducing the
pulp suspension
into the washer press at a drum inlet. The pulp suspension then moves within a
trough
adjacent to the drum.
100061 Washing and/or dewatering a liquid pulp suspension in a washer press
involves pressing the pulp suspension against at least one rotating
cylindrical drum in
order to separate some of the water and move this water out of the pulp
suspension into the
interior of the drum. As the pulp suspension is pressed against each drum, the
water or
other wash liquid is pressed through slots or perforations into the interior
of the drum and
a mat of pulp is formed and is typically scraped off by means of a scraper.
The pulp is
compressed within a trough formed between a pulp slide plate or the vat and
the exterior
surface of the drum. The width of the trough decreases and converges to form a
narrow
point, called a nip, such that the pulp suspension is compressed within the
narrowing
trough as it is moved by the rotation of the drum toward the nip.
[0007] Alternatively, the pulp suspension can be compressed mechanically by
moving the position of the pulp slide plate to decrease the distance between
the pulp slide
plate and the exterior surface of the drum, or this method can be combined
with other
compression methods. The compression of the pulp suspension by a movable or
fixed
pulp slide plate (a movable pulp slide plate is described in W02010/116026)
causes a
portion of water in the pulp suspension to be moved through the perforations
in the drum
into the interior of the drum.
[0008] In wash presses incorporating a nip and pulp slide plate, the pulp
suspension is most effectively washed immediately after it has been compressed
and
dewatered. In general in the industry, a goal is to achieve about an 8% to 10%
solids
concentration level in the pulp suspension at the nip point before the
suspension is washed.
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Although higher solids concentrations at the nip point, for example, up to
15%, would
yield an overall increase in the amount of impurities removed from the pulp
suspension,
such concentration increases are difficult to achieve due to problems with
clogging of the
trough.
100091 Attempted solutions to this problem have included the introduction of
additional washing at various intervals along the trough between a first, or
primary nip and
a last, or final nip to increase the level of impurities removed (a single
displacement wash
zone). The introduction of wash water in a single displacement wash zone,
however, does
not yield optimal results because the wash water merely mixes with existing
impurities. In
addition, the introduction of wash water into a single displacement wash zone
is less
controlled if added to the pulp suspension after it has passed the area
adjacent to the
primary nip. An addition of water in this manner also leads to decreased
dewatering of the
suspension at the end of the cycle. Movable pulp slide plates have also been
used to
alleviate clogs; however, washing efficiency is still limited by the physical
space within
which the washing must take place as the suspension moves around the drum.
10010] Accordingly, there is a need for an improved washing and dewatering
method and apparatus, more particularly a washing and dewatering method and
apparatus
with improved efficiency that is capable of washing and dewatering a wide
range of solids
concentrations in liquid suspensions. There is also a need for an improved
washing and
dewatering method and apparatus that provides increased impurity removal and
washing
capacity. There is a further need for an improved washing and dewatering
method and
apparatus that provides either standard washing results using less water, or
improved
washing results using a standard amount of water. There is still a need for a
washing and
dewatering method and apparatus that will accommodate a range of solids
concentrations
for processing. It is to these and other needs that the present invention is
directed.
BRIEF SUMMARY OF THE INVENTION
[0011] Briefly, the present invention comprises a washer press wherein a
liquid
suspension of a solid biological pulp material is fed to the washer press
using either a
mechanical distributor or a pressurized distributor to a drum that comprises
multiple
displacement wash zones between multiple nip points. The system allows for
controlled
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introduction of wash water or other appropriate liquid at an effective
location in the trough
and at a desirable solids concentration. The system further allows for the
removal of water
and impurities after an initial dewatering cycle, followed by an additional
compression and
washing cycle under optimum pulp washing conditions. The system in accordance
with
the present invention yields a standard solids consistency and an increased
purity level
using the same amount of water while avoiding problems caused by increasing
the surface
area of the outer drum surface in contact with the liquid pulp suspension (or
length) in the
displacement wash zone. The multiple nip multiple displacement wash zone
washer press
in accordance with the present invention allows for the processing of a wide
range of
solids concentrations. Therefore, the present invention provides in both
single and a twin-
drum washer presses increased washing efficiency with the versatility of
operating in
either a medium or low consistency process application.
[0012] Increased washing efficiency is achieved by providing a trough for pulp
distribution using multiple pulp slide plates to direct the liquid pulp
suspension into the
trough and along a drum surface. The pulp suspension is fed into the trough by
means of a
pulp distributor, such as a mechanical distributor for medium consistency
suspensions or
pressure distributor for low consistency suspensions, to evenly disperse the
pulp along the
full length of the trough to form an even pulp mat.
100131 The mechanical pulp distributor consists of a tapered, center feed
reverse
flighted screw that evenly distributes the pulp along the length of the drum.
The pressure
pulp distributor comprises a pressure headbox with changeable orifices to
create an even
pulp formation. Both distributors can be bolted to an existing washer press
vat. The
distributor has a longitudinal seal and end seals to separate the product from
the
atmosphere. In an alternative embodiment, the distributor housing has a first
pulp slide
plate, which can be static or adjustable or movable thereby creating an upper
nip point. A
second pulp slide plate, which can also be static or adjustable thereby
creating a lower nip
point, may be incorporated to allow for a second displacement wash zone along
the drum.
In an exemplary embodiment, the location at which the pulp suspension enters
and
contacts the surface of the drum is adjusted such that the surface area of the
outer drum
surface in contact with the liquid pulp suspension is increased by 15% to 25%,
and
preferably 15% to 20%, compared with conventional designs. Therefore, the
method and
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use of the apparatus, in an exemplary embodiment, could result in the pulp
suspension
contacting 65% to 75% of the total surface area of the drum, where only about
50% of the
surface area of the drum is contacted in conventional applications.
100141 As the pulp suspension enters and contacts the outer drum surface, a
movable or static pulp slide plate directs the pulp suspension along the outer
drum surface
where dewatering begins. Dewatering continues as the liquid pulp suspension is
moved
between the walls of the trough by the rotation of the drum to a first point
of constriction
in the trough, called the primary nip. The primary nip is the point in the
trough
downstream from the drum inlet having the narrowest width. Although the width
of the
trough at the primary nip is narrow, the width of the trough immediately after
and
downstream from the narrowed nip point increases at the first release point,
where the first
stream of wash water or other liquid is added. This introduction of wash water
or other
liquid in a first displacement wash zone allows the solids within the pulp
suspension to be
washed and continually dewatered as they pass the length of the first
displacement wash
zone, which is defined by the outer drum surface and a second pulp slide plate
as the sides,
and the first release point and a secondary nip as the ends. In one
embodiment, the first
displacement wash zone located between the primary nip and the secondary nip
contacts
about 20 to 25% of the surface area of the drum. In another embodiment, the
width of the
primary nip can be adjusted, for example, by changing the position of an
adjustable pulp
slide plate.
100151 In an exemplary embodiment, the width of the trough immediately after
and downstream from the secondary nip increases. This area is called the
second release
point, which is the beginning of a second displacement wash zone in the trough
having the
smallest opening dimension. Although the width of the trough at the secondary
nip is the
narrowest within the first displacement wash zone, the width of the trough
beginning at the
second release point is increased and forms a third segment (the second
displacement wash
zone). The second displacement wash zone is defined by the vat and the drum
outer
surface on the sides, the second release point on one end, and a final nip at
the other end.
100161 Wash water or other liquid is again added at the second release point
downstream from the secondary nip, and the pulp suspension is continually
washed and
dewatered as the pulp is pulled by the drum through the second displacement
wash zone of
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the trough, terminating at the area of the trough in the second displacement
wash zone
having the narrowest width: the final nip. The second displacement wash zone
allows for
the displacement of the first displacement wash water (or other liquid) and
the impurities
contained therein, and it allows for the introduction of second displacement
wash water (or
other liquid), thus creating a more effective wash and contaminant removal. In
accordance
with an embodiment of the method described herein, the final solids
concentration of the
resultant fiber mat reaching the final nip is approximately 30% to 35%, and in
another
embodiment, is 30% to 33%. In another embodiment, the width of the trough at
the
secondary and final nips can be adjusted, for example, by changing the
position of an
adjustable pulp slide plate. As an illustrative example, the width of the
secondary nip can
be the greatest, followed by the width of the primary nip, and then the width
of the final
nip. The width of the nips can be adjusted to optimize solids concentration
and to prevent
blockage.
[0017] These features, and other features and advantages disclosed herein will
become more apparent to those of ordinary skill in the art when the following
detailed
description of the preferred embodiments is read in conjunction with the
appended figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a partial sectional end view of a conventional washer press.
[0019] FIG. 2 is a partial sectional end view of a washer press in accordance
with the present invention incorporating a primary, secondary, and final nip
into a
mechanical pulp distributing system.
[0020] FIG. 3 is a partial sectional end view of a washer press in accordance
with the present invention incorporating a primary, secondary, and final nip
into a pressure
pulp distributing system.
[0021] FIG. 4 is a side perspective view of a pulp inlet for a pressure pulp
distributing system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
100221 The foregoing detailed description of the preferred embodiments is
presented only for illustrative and descriptive purposes and is not intended
to be
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exhaustive or to limit the scope and spirit of the invention. The embodiments
were
selected and described to best explain the principles of the invention and its
practical
application. One of ordinary skill in the art will recognize that many
variations can be
made to the invention disclosed in this specification without departing from
the scope and
spirit of the invention.
[0023] Illustrative embodiments of a washer press with multiple nips in
accordance with the disclosure are shown in FIGs. 2 ¨ 3. The present invention
is a
multiple nip multiple displacement wash zone washer press suitable for use in
conjunction
with a pulp dewatering system, and methods for using same. Currently, there is
a need for
a pulp dewatering system that provides increased efficiency and purity while
accommodating pulp suspensions having a wide range of solids concentrations.
[00241 An invention has been developed for a pulp suspension washer press
having at least one drum with an exterior drum surface disposed within a vat;
a pulp
distributor having a pulp inlet adjacent to the drum; at least one pulp slide
plate adjacent to
the exterior drum surface; a trough having two sides and two ends, where the
trough sides
comprise the exterior drum surface on one side and the pulp slide plate or the
vat on the
other side. The trough ends comprise a pulp inlet on one end and a nip on the
other end,
and there are at least two displacement wash zones within the trough, where
the
displacement wash zones each have a first end and a second end, and where each
first and
second end of the displacement wash zones comprise a nip.
100251 Another embodiment of the invention has been developed for a pulp
suspension washer press having at least one drum with an exterior drum surface
disposed
within a vat; a pulp distributor having a pulp inlet adjacent to the drum;
multiple pulp slide
plates adjacent to the exterior drum surface; a trough having two sides and
two ends,
where the trough sides comprise the exterior drum surface on one side and at
least one
pulp slide plate or the vat on the other side. The trough ends comprise a pulp
inlet on one
end and a nip at the other end, and at least two displacement wash zones are
within the
trough. The displacement wash zones each have a first end and a second end,
where each
first and second end of the displacement wash zones is adjacent to a nip, and
the width of
each nip within the trough is less than the width of the remainder of the
respective trough
sections comprising the displacement wash zones.
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[0026] A method has also been developed for washing and dewatering a liquid
pulp suspension which includes feeding a liquid pulp suspension into a pulp
distributor;
placing a drum inlet attached to the pulp distributor at a location along an
exterior drum
surface of a drum such that liquid pulp suspension fed into the pulp
distributor and
contacting the exterior drum surface through the drum inlet contacts 65% to
75% of the
entire surface area of the exterior drum surface, whereby multiple
displacement wash
zones are created in the area of the exterior drum surface contacted by the
liquid pulp
suspension.
[0027] Additionally, another method has been developed for washing and
dewatering a liquid pulp suspension which includes feeding a liquid pulp
suspension into a
trough between an exterior drum surface and a pulp slide plate; guiding the
pulp
suspension into a first zone within the trough with a first pulp slide plate;
simultaneously
moving and dewatering the pulp suspension through the first zone with a
rotating drum;
concentrating the pulp suspension at a primary nip; guiding the pulp
suspension into a first
displacement wash zone adjacent the primary nip; simultaneously moving,
washing, and
dewatering the pulp suspension through the first displacement wash zone;
concentrating
the pulp suspension at a secondary nip; guiding the pulp suspension into a
second
displacement wash zone within the trough; adding a second volume of wash
liquid into the
second displacement wash zone adjacent the secondary nip; simultaneously
moving,
washing, and dewatering the pulp suspension through the second displacement
wash zone;
and concentrating the pulp suspension at a final nip, to form a pulp mat.
[0028] In one embodiment of the present invention, the placement of a
mechanical or pressure distributor to feed the pulp suspension into the washer
press
provides an advantageous result in the dewatering process. In this embodiment,
the
position of the pulp distributor is adjusted to allow for an increase in the
angle at which the
suspension is fed to the drum (the feed angle), allowing for an increased
dewatering region
and additional contact duration to form a quality fiber mat along the exterior
surface of the
drum.
[0029] Referring now to FIG. 1, which illustrates a conventional washer press
1
comprising a drum 5 and other critical features. The conventional washer press
1 is of a
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twin drum configuration (the left drum is partially shown), but a single drum
washer press
and other configurations are known in the art. A pulp suspension enters the
conventional
washer press 1 at a pulp inlet 10, and is transported to a drum inlet 15. A
trough 20 is
located between the drum inlet 15 and a primary nip 25 formed on one side by
an outer
drum surface 30, and on the other side by a pulp slide plate 35. The pulp
suspension is
dewatered as it moves within the trough 20 toward the primary nip 25.
[0030] At the primary nip 25, wash water 37 or other liquid is added from a
water header 40 into the pulp suspension in a displacement wash zone 45. This
wash
water 37 allows the solids in the suspension to be washed as the suspension is
continuously dewatered. As the pulp suspension moves through the displacement
wash
zone 45 to a final nip 50, the suspension is both washed and dewatered because
the
distance between the outer drum surface 30 on one side, and a vat 55 on the
other side, is
reduced, which compresses the suspension and separates the liquid from the
pulp
suspension. The narrowest point of the displacement wash zone 45 within the
trough 20 is
the final nip 50.
[0031] Washing and dewatering simultaneously occurs as the pulp suspension
moves through the trough 20 and away from the drum inlet 15, by the rotation
of the drum
5, until the final nip 50 is reached. At this point, the liquid pulp
suspension has been
concentrated and a pulp mat has formed on the outer drum surface 30. The
liquid
separated from the compressed pulp suspension is passed through the outer drum
surface
30 into the drum interior 60, where the liquid then exits the washer press 1.
[0032] Referring now to FIG. 2, a washer press 101 in accordance with an
embodiment of the present invention in conjunction with a mechanical pulp
distributor
109 can be used to feed a medium-consistency pulp suspension having, for
example, a
consistency of about 2.5% to about 11% solids, or about 2.5% up to about 15%
solids, into
the washer press 101. The washer press 101 comprises a drum 105 having a drum
inlet
115 positioned adjacent the drum 105. The pulp suspension enters the washer
press 101 at
a pulp inlet 110, is fed through the mechanical pulp distributor 109, and then
enters a
trough 120 through a drum inlet 115. In an exemplary embodiment, the position
of the
drum inlet 115 and the mechanical pulp distributor 109 are adjusted to allow
for an
increase in the angle at which the suspension is fed into the drum 105 such
that the
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distance between the drum inlet 115 and a final nip 150, as measured along the
circumference of an exterior drum surface 130, has increased between 15% and
30% as
compared to the distance between these points on a conventional wash press 1
(as shown
in FIG. 1). Further, the drum inlet 115 is positioned such that the total
surface area of the
exterior drum surface 130 contacted by the pulp suspension is increased
between 15% and
30% as compared with a conventional wash press 1 (as shown in FIG. 1).
[0033] The mechanical pulp distributor 109 comprises a tapered, center feed
reverse flighted screw that evenly distributes the pulp along the surface of
the drum 105.
The mechanical pulp distributor 109 can be bolted to an existing washer press
vat or other
suitable location. The mechanical pulp distributor 109 has a longitudinal seal
and end
seals to separate the product from the atmosphere. In an alternative
embodiment, the
distributor housing has an adjustable plate as known as a first pulp slide
plate 135. A
second pulp slide plate 136 may be incorporated to allow for additional
washing zones
along the trough 120. In other alternative embodiments, the first and second
pulp slide
plates 135 and 136 can be fixed or adjustable.
100341 The liquid pulp suspension flows through the trough 120 across the
exterior drum surface 130, and is guided by the fixed or movable first pulp
slide plate 135
where dewatering begins. The trough 120 has been formed by the first pulp
slide plate
135 and a second pulp slide plate 136 on one side, and the exterior drum
surface 130 on
the other side, and the length of the trough 120 extends from the drum inlet
115 to the final
nip 150. Dewatering continues as the liquid pulp suspension is pulled through
the trough
120 by the rotation of the drum 105 through a first zone ending at the
narrowest point in
the trough 120 downstream from the drum inlet 115, the primary nip 125. As the
pulp
suspension moves from the drum inlet 115 to the primary nip 125, the distance
between
the exterior drum surface 130 and the first pulp slide plate 135 is reduced in
order to
dewater the suspension by separating a portion of water from the pulp
suspension.
Although the primary nip 125 is the point in the first zone of the trough 120
with the
smallest width, the width of the trough 120 immediately after and downstream
from the
primary nip 125 widens again to a second section in the trough 120 having a
width larger
than that of the primary nip 125, called the first release point 127. The pulp
suspension is
dewatered when the water squeezed and separated from the suspension is passed
through
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the exterior drum surface 130 into the drum interior 160, where the water then
exits the
washer press 101.
100351 At the first release point 127, a first stream or volume of wash water
137
or other liquid is added to the washer press 101 from a first water header
140. This wash
water 137 or other liquid allows the solids in the suspension to be washed
while
continuously being dewatered. The first stream of wash water 137 can be fresh,
or can be
recycled from elsewhere in the plant. As the solids mixed with the wash water
137 move
along the exterior drum surface 130 toward the final nip 150, a second pulp
slide plate 136
is positioned in a first displacement wash zone 145 located between the first
release point
and a secondary nip 126. In another exemplary embodiment, the second pulp
slide plate
136 is fixed rather than movable.
100361 In this embodiment, the location of the first displacement wash zone
145
is defined by the exterior drum surface 130 and a second pulp slide plate 136
as the sides,
and the first release point and the secondary nip 126 at each end. In another
exemplary
embodiment, the first displacement wash zone 145 located between the primary
nip 125
and the secondary nip 126 contacts about 20% to 30% of the surface area of the
drum 105.
The width of the trough 120 at the primary or secondary nips 125 or 126 can be
adjusted
by changing the position of adjustable first or second pulp slide plates 135
or 136.
100371 The solids in the pulp suspension are washed and the suspension is
dewatered simultaneously as the suspension moves through the first
displacement wash
zone 145 between the primary nip 125 and the secondary nip 126. A second
stream or
volume of wash water 137 or other liquid is introduced to the liquid pulp
suspension
through a second water header 141 at or about a point in the trough 120
immediately after
and downstream from the secondary nip 126, called the second release point
147.
[0038] At the second release point 147, the width of the trough 120 increases
again to begin a third section in the trough 120 having a width larger than
that of the
secondary nip 126. The solid material is then subjected to a second washing
cycle, with
continuous dewatering, in a second displacement wash zone 146. The second
displacement wash zone 146 is located between the second release point 147 and
the final
nip 150 at the ends, and the exterior drum surface 130 and a vat 155 at the
sides. The
second wash water 137 used in the second displacement wash zone 146 can be
fresh, or
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recycled from elsewhere in the plant. At the final nip 150, the liquid pulp
suspension has
been concentrated to a solids consistency of approximately 30% to 35%, and a
pulp mat
has formed on the exterior drum surface 130. The liquid separated from the
compressed
pulp suspension is passed through the exterior drum surface 130 into the drum
interior
160, where the liquid then exits the washer press 101.
[0039] The second displacement wash zone 146 allows for the displacement of
the first wash water 137 and the impurities contained therein and the
introduction of
second wash water 137, thus creating a more effective wash and contaminant
removal. In
accordance with an alternative embodiment of the method of the present
invention, the
final solids concentration of the resultant fiber mat reaching the final nip
150 is
approximately 30% to 33%. In another embodiment of an apparatus in accordance
with
the present invention, the width of the secondary nip 126 can be the greatest
as between
the widths of each of the other multiple nips, followed by the primary nip
125, with the
final nip 150 having the smallest width. The width of the nips can be adjusted
to optimize
solids concentration and to prevent plugging or blockage. Although the washer
press 101
in some exemplary embodiments is of a side-by-side twin-drum washer press
configuration, or a bottom-to-top twin drum or a single drum configuration,
other
configurations known in the art are suitable for use in conjunction with the
present
invention. The method and apparatus in accordance with the present invention
produce
the same or better results as conventional methods and apparatuses, while
increasing the
efficiency of the washer press and yielding a pulp mat that can be as great as
18% more
purified. Additionally, this apparatus can result in increased production
capacity by as
much as 30%.
[0040] Turning now to FIG. 3, a washer press 201 in accordance with another
embodiment of the disclosure in conjunction with a pressure pulp distributor
209 and 301
(FIG. 4) can be used to feed a low-consistency pulp suspension having, for
example, a
consistency of about 2.5% to about 5% solids, into the washer press 201.
Washer press
201 comprises a drum 205 having a drum inlet 215. The pulp suspension enters
the
washer press 201 at a pulp inlet 210, is fed through the pressure pulp
distributor 209, and
then enters the trough 220 through the drum inlet 215. Drum inlet 215 is
positioned along
an exterior drum surface 230 such that the distance between the drum inlet 215
and a final
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nip 250, as measured along the circumference of the exterior drum surface 230,
has
increased between 15% and 30% as compared to the distance between these points
on a
conventional wash press 1 (FIG. 1).
[0041] The pressure pulp distributor 209 and 301 (FIG. 4) is comprised of a
pressure headbox with changeable orifices to create an even pulp suspension
formation.
The pressure pulp distributor 209 and 301 can be bolted to an existing washer
press vat or
other suitable structure. The pressure pulp distributor 209 and 301 has a
longitudinal seal
and end seals to separate the product from the atmosphere. The pressure pulp
distributor
209 and 301 have the pulp inlet 210 and 310 (FIG. 4) attached to allow pulp
suspension to
be fed to the washer press 201.
[0042] The liquid pulp suspension flows through the trough 220 across the
exterior drum surface 230. Trough 220 has been formed by a movable or fixed
first pulp
slide plate 235 and a second pulp slide plate 236 on one side, and the
exterior drum
surface 230 on the other side, and the length of the trough 220 extends from
the drum inlet
215 to the final nip 250. As the pulp suspension moves from the drum inlet 215
to a
primary nip 225, the distance between the exterior drum surface 230 and the
first pulp
slide plate 235 is reduced in order to dewater the suspension by separating a
portion of the
water from the pulp. The pulp suspension is dewatered when the water squeezed
and
separated from the suspension is passed through perforations in the exterior
drum surface
230 into a drum interior 260, where the water then exits the washer press 201.
[0043] Immediately after and downstream from the primary nip 225, wash water
237 or other liquid is added to the washer press 201 from a first water header
240 at a first
release point 227. This wash water 237 allows the solids in the suspension to
be washed
and dewatered. As the solids and wash water 237 move along the exterior drum
surface
230 toward the final nip 250, a movable or fixed second pulp slide plate 236
is positioned
in a first displacement wash zone 245 located between the first release point
227 and a
secondary nip 226. In another exemplary embodiment, the second pulp slide
plate 236
comprises a second movable pulp slide plate. In yet another exemplary
embodiment, the
second pulp slide plate 236 comprises a fixed pulp slide plate while the first
pulp slide
plate 235 comprises a fixed pulp slide plate.
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[0044I The solids in the suspension are washed and the suspension is
simultaneously
dewatered as the suspension moves through the first displacement wash zone 245
between
the first release point 227and the secondary nip 226. A second volume of wash
water 237 is
introduced to the liquid pulp suspension through a second water header 241
into the trough
220 immediately after and downstream from the secondary nip 226, called the
second release
point 247. The solid material is subjected to a second washing cycle and is
simultaneously
dewatered in a second displacement wash zone 246, defined by the second
release point 247
and the final nip 250 at the ends, and the exterior drum surface 230 and the
vat 255 at the
sides. At the final nip 250, the suspension has been concentrated to a solids
consistency of
approximately 30% to 35%, or approximately 30% to 33%, and a pulp mat has
formed on the
exterior drum surface 230. A doctor blade (not shown) is used to remove the
pulp mat from
along the exterior drum surface 230.
10045) Thus, a number of preferred embodiments have been fully described above
with reference to the drawing figures. The scope of the claims should not be
limited by the
preferred embodiments and examples, but should be given the broadest
interpretation
consistent with the description as a whole.
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